In 1996, the total harvest of domestic crabs reached nearly 400,000,000 pounds. This figure represents both commercial and recreational harvests. The principle method for harvesting crabs is by using baited crab traps. Because different types of crabs reside in different environments, crab traps are used in a variety of bottom conditions ranging from flat sandy bottoms to rocky, uneven bottoms with large kelp beds. In some circumstances, traps are often left unattended for several hours or longer; in other circumstances, the traps are checked and the catch harvested as often as every few minutes.
Over the years, there have been many inventions relating to crab or other underwater animal traps and their methods of construction. Such traps were normally lowered from a boat deck or other above-water surface to the floor, after being baited, and were originally made of box-like wooden frames stretched with a netting or mesh material. Updates and changes have been made to the shape, material, and operation of the crab traps with varying degrees of success. As a result of either ingenuity or marketing efforts, there are many shapes and types of crab traps in use today, including pyramidal, conical, and rectangular shapes. One of modifications is an "A"-frame or triangular prism-type with a wide bottom, an apex top, and triangular sides. The wide bottom helps to ensure that the crab trap rests securely on the ocean floor in the upright position, and the apex top helps to ensure that the crab trap can be raised through the water by its retrieval line with decreased chances of getting fouled in seaweed or other debris.
Collapsibility for ease of storage is a feature of most recreational crab traps presently in production. Furthermore, crab traps are now made of more durable materials than the original wood: they are usually of metal frames with metal wire mesh. The wires are then coated with an appropriate material to make handling easier and to prevent exposure of the metal to the water. However, at least one patented invention, U.S. Pat. No. 4,982,525, suggests that plastic could be used for the frames and mesh.
Additionally, many recent inventions relate to the opening of the crab trap once it is underwater and ready to be used. End panels are often spring-loaded or weighted to provide positive opening. The spring-loading of a trap may be provided by a coil spring wrapped around the bottom of the side and bottom frames and effects positive opening by applying an outward bias against the end panels. Alternatively, weighted end panels use gravity to pull the panels open and keep them in the open position.
Although the above-mentioned improvements have enhanced the operation and use of crab traps, many problems remain, including difficulty and danger in removing the catch. In many instances, the trapsetter must take the catch out of the crab trap through the same openings through which the catch entered the trap. Alternatively, the crab trap may be such that the trapsetter must nearly collapse the entire trap in order to gain access to the catch. In this case, the trap no longer is retaining the catch and the possibility exists that the catch will escape.
Furthermore, the crab trap may foul in itself due to its own construction. The tips of a triangular configured trap (whether pyramidal or A-frame) many interfere with other trap components when the side panels are pulled into the closed position for retrieval of the trap. Such fouling increases the difficulty of opening the side panels for harvesting the catch.
Additionally, metal hinges used on many traps are subject to corrosion and therefore present further problems. Corroded hinges may seize and prevent not only the safe and easy operation of the crab traps but also the proper collapsing of the crab traps for stowage.